<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title></title>
</head>
<body>
<table>
  <tr>
   <td><input type="button" value="add"   onclick="setOp('+', 'add');"/></td>
   <td><input type="button" value="inner" onclick="setOp('-', 'inner');"/></td>
  </tr>
</table>
<table id="tb_calc" style="display:none;">
   <tr>
    <td> <input id="x" type="text" style="width:100px" value="" name="x" /></td>
    <td> <lable id="op" name="op"></lable> </td>
    <td> <input id="y" type="text" style="width:100px" value="" name="y" /> </td>
    <td> <input id="opTips" type="button" value="" onclick="calc();"/> </td>
    <td> <lable id="z" name="z"></lable> </td>
  </tr>
</table>
<script type="application/javascript">
  function setOp(op, opTips)
  {
    var tb=document.getElementById("tb_calc");
    tb.style.display = "none";
          
    document.getElementById("x").value = ""; 
    document.getElementById("y").value = ""; 
    document.getElementById("z").innerText = ""; 
    document.getElementById("op").innerText = op;
    document.getElementById("opTips").value = opTips;
    
    tb.style.display = "block";
  }
  function calc()
  {
    var x = parseInt(document.getElementById("x").value); 
    var y = parseInt(document.getElementById("y").value);
    var op = document.getElementById("op").innerText;
    
    var z = "";
      switch(op)
      {
        case '+':
          z = x + y;
          break;
        case '-':
          z = x - y;
         break;
      }
    console.log(x, op, y, '=', z);
    document.getElementById("z").innerText = z;
  }
</script>
</body>
</html>